We haven't seen PIL of more than 5 years.
DS1 was 2.5 and DS2 6m. After many years of tension, they decided they wanted nothing more to do with us and DH decided life was easier without them, which it is, although I find that incredibly sad. Nothing I say can persuade him to get in touch, although I have tried to keep the lines of communication open by sending birthday & Christmas cards and photos.
To begin with PIL said rather than post presents for our DCs, they would open bank accounts and make deposits at birthday/Christmas, which was obviously their choice, although I never realy expected Dcs to see the money.
Then they started sending cash in the cards. To begin with, I sent thank you notes and paid the gifts into Dcs accounts, without Dcs being aware of it.
Now they're getting older, I feel they should know of their GPs existance and as they are aware of what's going in and out of their bank accounts, they should know the source and write their own thank you notes.
DH doesn't want DCs to have anything to do with them, but doesn't want to send the gifts back and cause "trouble". It's not about the cash - our children hardly go without and TBH wouldn't miss it if they didn't get it, but PIL would take huge offence if we sent it back.
So, on the basis that the Dcs keep it, should they write thank you letters even though they don't know the people they'll be writing to?